<!doctype html>
<meta charset="utf-8">
<script>
const dbName = "users";

// Create the database at v1 and detect success via `onsuccess`.
function createDatabase() {
  return new Promise((resolve, reject) => {
    var dbRequest = window.indexedDB.open(dbName, 1);
    dbRequest.onblocked = () => reject();
    dbRequest.onerror = () => reject();
    dbRequest.onsuccess = (e) => {
      e.target.result.close();
      resolve();
    }
  });
}

// Open the database at v2 and detect existance via `onupgradeneeded`.
function doesDatabaseExist() {
  let didExist = false;
  return new Promise((resolve, reject) => {
    var dbRequest = window.indexedDB.open(dbName, 2);
    dbRequest.onblocked = () => reject();
    dbRequest.onerror = () => reject();
    dbRequest.onsuccess = (e) => {
      e.target.result.close();
      deleteDatabase().then(() => resolve(didExist));
    };
    dbRequest.onupgradeneeded = (e) => {
      didExist = e.oldVersion != 0;
    };
  });
}

// Delete the database and detect success via `onsuccess`.
function deleteDatabase() {
  return new Promise((resolve, reject) => {
    var dbRequest = window.indexedDB.deleteDatabase(dbName);
    dbRequest.onblocked = () => reject();
    dbRequest.onerror = () => reject();
    dbRequest.onsuccess = () => resolve();
  });
}

// Step 2
window.addEventListener("load", () => {
  parent.postMessage(
    {message: "iframe loaded"},
    "*",
  );
});

window.addEventListener("message", (e) => {
  if (e.data.message == "create database") {
    // Step 4
    createDatabase().then(() => {
      parent.postMessage(
        {message: "database created"},
        "*",
      );
    });
  } else if (e.data.message == "check database") {
    // Step 6
    doesDatabaseExist().then((result) => {
      parent.postMessage(
        {
          message: "database checked",
          doesDatabaseExist: result,
        },
        "*",
      );
    });
  }
});
</script>
